A sweep frequency signal is typically used in a broadcast and communication system. A sweep frequency signal is usually generated by using a frequency reference source, a voltage controlled oscillator, a phase detector and a phase locked loop (PLL) comprising a filter feedback loop, the four parts being referred as a frequency synthesizer in combination. The width of the swept frequency of the PLL is limited by the operating frequency range of the voltage controlled oscillator. Noise in the sweep frequency signal is dependent on the time for sweeping of frequency. A long time for locking is needed for a low noise level, while the noise is large in order to obtain a quick sweep frequency output signal.